U.S. patent number 4,210,819 [Application Number 05/934,574] was granted by the patent office on 1980-07-01 for open cycle ocean thermal energy conversion steam control and bypass system.
This patent grant is currently assigned to The United States of America as represented by the United States. Invention is credited to Stephen J. Jennings, J. Michael Wittig.
United States Patent |
4,210,819 |
Wittig , et al. |
July 1, 1980 |
Open cycle ocean thermal energy conversion steam control and bypass
system
Abstract
Two sets of hinged control doors for regulating motive steam
flow from an evaporator to a condenser alternatively through a set
of turbine blades in a steam bypass around the turbine blades. The
evaporator has a toroidal shaped casing situated about the
turbine's vertical axis of rotation and an outlet opening therein
for discharging motive steam into an annular steam flow path
defined between the turbine's radially inner and outer casing
structures. The turbine blades extend across the steam flow path
intermediate the evaporator and condenser. The first set of control
doors is arranged to prevent steam access to the upstream side of
the turbine blades and the second set of control doors acts as a
bypass around the blades so as to maintain equilibrium between the
evaporator and condenser during non-rotation of the turbine. The
first set of control doors preferably extend, when closed, between
the evaporator casing and the turbine's outer casing and, when
open, extend away from the axis of rotation. The second set of
control doors preferably constitute a portion of the turbine's
outer casing downstream from the blades when closed and extend,
when open, toward the axis of rotation. The first and second sets
of control doors are normally held in the open and closed positions
respectively by locking pins which may be retracted upon detecting
an abnormal operating condition respectively to permit their
closing and opening and provide steam flow from the evaporator to
the condenser.
Inventors: |
Wittig; J. Michael (West
Goshen, PA), Jennings; Stephen J. (Radnor Township, Delaware
County, PA) |
Assignee: |
The United States of America as
represented by the United States (Washington, DC)
|
Family
ID: |
25465743 |
Appl.
No.: |
05/934,574 |
Filed: |
August 17, 1978 |
Current U.S.
Class: |
290/52; 290/1R;
60/641.7 |
Current CPC
Class: |
F03G
7/05 (20130101); Y02E 10/34 (20130101); Y02E
10/30 (20130101) |
Current International
Class: |
F03G
7/00 (20060101); F03G 7/05 (20060101); F03G
007/04 () |
Field of
Search: |
;290/1,2,52
;60/641,671 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Andrew Nizery-"Study of the Possibility of the Utilization of
Thermal Energy of the Sea and of Solar Energy", Bulletin _de
l'Institute Oceanographique No. 906, Dec. 30, 1946..
|
Primary Examiner: Rubinson; Gene Z.
Assistant Examiner: Duncanson, Jr.; W. E.
Attorney, Agent or Firm: Keen; J. W.
Government Interests
GOVERNMENT CONTRACT
This invention is believed to have been made or conceived in the
course of, or under a contract with the United States Department of
Energy identified as EG-77-03-1473.
Claims
What we claim is:
1. An open cycle ocean thermal energy conversion system
comprising:
an axial flow turbine having a rotor whose axis of rotation is
vertical and radially inner and outer casing structures which
therebetween define an annular motive fluid path, said rotor
including an annular array of radial blades extending across said
fluid path;
a condenser in fluid communication with said annular motive fluid
flow path for condensing the motive fluid expanded through the
turbine blades;
a flash evaporator disposed about the turbine's axis of rotation,
said evaporator having a generally toroidal-shaped casing, the
interior of said casing being in fluid communication with said
condenser both through and in bypassing relationship with said
turbine blades;
first means for regulating motive fluid flow from said evaporator
to said condenser through said turbine blades; and
second means for regulating bypass motive fluid flow from said
evaporator to said condenser.
2. The system of claim 1, said first regulating means
comprising:
a control wall disposed between said evaporator casing and said
turbine's outer casing structure, said wall having ports therein
for transmitting motive fluid therethrough;
a plurality of hinged access control doors for selectively
obstructing said ports against motive fluid flow therethrough;
locking means for releasably retaining said control doors in an
open position; and
means for selectively actuating said locking means.
3. The system of claim 2, wherein said control doors, when open,
extend away from said axis of rotation.
4. The system of claim 2, said locking means comprising a plurality
of pins displaceable between positions which obstruct and permit
door closure.
5. The system of claim 1, said second regulating means
comprising:
a plurality of ports in said turbine's outer casing structure
downstream from said blades permitting fluid communication between
said evaporator and said turbine's annular fluid path;
a plurality of hinged bypass control doors for selectively
obstructing said ports against motive fluid flow therethrough;
locking means for releasably retaining said bypass control doors in
a closed position; and
means for selectively actuating said locking means.
6. The system of claim 5, wherein said bypass control doors, when
open, extend toward the axis of rotation.
7. The system of claim 5, said locking means comprising a plurality
of pins displaceable between positions which obstruct and permit
bypass door opening.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This invention is related to inventions disclosed in the
applications of J. M. Wittig, Ser. Nos. 934572 and 934575, whose
filing dates are both Aug. 17, 1978.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to open cycle, ocean thermal energy
conversion systems, and more particularly, to a steam flow control
and bypass arrangement for regulating motive steam flow through a
turbine component of the open cycle OTEC systems.
2. Description of the Prior Art
Ocean thermal energy conversion is a process by which the normal
temperature difference existing between relatively warm surface
waters and relatively cold, subsurface waters is utilized to
develop a pressure difference across a turbine through which a
motive fluid is expanded. The surface of large water bodies, such
as oceans, acts as a large solar energy collector for heating the
exposed water. The solar heated water is partially flashed into
steam which acts as the cycle's motive fluid. The motive fluid's
expansion through the turbine causes the turbine's rotor structure
to rotate. A generator suitably coupled to the turbine's rotor
rotates therewith and produces electrical energy. Due to the small
temperature and pressure differences typically found in ocean
thermal energy conversion cycles (30.degree. F. and 0.3 psi by
example), the cycle efficiencies are rather low. Since no fuel is
consumed, the cost of operation for an ocean thermal energy
conversion system is substantially reduced over conventional cycles
and the primary factor limiting their use is the capital and
construction costs of the equipment components. Components such as
the turbine and heat exchangers must, by necessity, be very large
to yield reasonable net electrical power output.
Ocean thermal energy conversion systems are typically classified to
be of the open and closed cycle variety in which seawater and other
volatile fluids are respectively utilized for the motive fluid.
While the cycle varieties each have certain advantages over the
other, a primary disadvantage of the open cycle OTEC has been the
extremely large floating platform or hull structures required to
support the power generation equipment and the high cost for
materials and construction thereof. Reduction in the size and cost
of the large platform structures required for open cycle OTEC power
systems could provide a favorable advantage for such open cycles
when compared with closed cycle OTEC systems. Platform elimination
and/or size reduction was disclosed in J. M. Wittig's commonly
assigned patent application Ser. No. 934,575. Such platform
elimination utilizes optimum relative equipment disposition and
integrates the equipment casings and supporting platform into one
structure of complex shape. Due to the functional integration of
the equipment casings and supporting platform, the resulting
complexly shaped structure lent itself to fabrication from
prestressed concrete. A fast responding steam flow control device
for installation therein was sought to prevent turbine-generator
overspeed after full load dump. It was determined that the flashed
steam must be diverted around the turbine to reduce its torque and
acceleration to zero as well as maintain evaporator-condenser
equilibrium. An annular vane structure for bypassing steam through
an annulus between rotatable turbine blades and the turbine's
casing as disclosed in B. L. LaCoste's copending patent application
Ser. No. 918,127 was considered. Such annular vane structure's
adaptation to J. M. Wittig's functionally integrated system
structure was judged economically unfeasible. System vacuum
reduction, as also disclosed in patent application Ser. No.
918,127, presented a disadvantage of exerting excessive pressure
loads on the complexly shaped prestressed concrete system
structure. Furthermore, the large steam volumetric flow rates
typically encountered in open cycle OTEC systems render the use of
conventional stop valves for Wittig's functionally integrated
system structure impractical due to their excessive size, pressure
drop, inertia, and response time.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved open cycle
ocean thermal energy conversion system is provided for generating
electrical power and producing distilled water. The invention
generally comprises an axial flow turbine having a vertical shaft
with an annular motive fluid flow path situated thereabout and an
array of blades connected to the shaft and extending across the
flow path, a condenser in fluid communication with the fluid path
for condensing the motive fluid expanded through the turbine
blades, a flash evaporator whose toroidal casing's interior is in
fluid communication with the condenser both through the turbine
blades and in bypassing relationship therewith, and first and
second means for regulating motive fluid flow from the evaporator
to the condenser alternatively through the turbine blades and in
bypassing relationship therewith.
In a preferred embodiment of the invention, the motive fluid
regulating means constitute a first and a second set of control
doors respectively mateable with a first and second set of control
ports. The first set of control doors preferably extend, when
closed, across the steam flow path upstream from the turbine blades
between the evaporator casing and the turbine's outer casing
structure and the second set of control doors constitute, when
closed, a part of the turbine's outer casing structure downstream
from the blades. The first and second sets of control doors are
preferably held in their respectively normally open and closed
positions by locking pins which are retractable, upon detection of
an abnormal operating condition, to permit their closing and
opening respectively from forces exerted thereon by the motive
fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following
detailed description of a preferred embodiment, taken in connection
with the accompanying drawings, in which:
FIG. 1 is an elevation view of an open cycle OTEC system
structure;
FIGS. 2A and 2B are sectional views of FIG. 1 illustrating
alternate condenser tube arrangements;
FIG. 3 is a cutaway pictorial illustration of the system shown
sectioned in FIG. 2B;
FIG. 4 is a pictorial illustration of a portion of the evaporator
illustrated in FIGS. 2A and 2B;
FIGS. 5A, 5B, and 5C illustrate control doors for diverting steam
away to or away from the system turbine; and
FIGS. 6A and 6B illustrate alternate plan views of an outer
skirt-conduit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 an OTEC open cycle system structure 10 is shown, disposed
in operating position within a body of water such as an ocean with
the illustrated representative submergence of the structure 10
within the ocean. Cold supply water conduit 12 is illustrated in a
discontinuous manner since it extends approximately one thousand
meters below the ocean's surface which is indicated by reference
numeral 14. Cold water conduit 12 preferably constitutes
prestressed concrete and rubber sections which are respectively
disposed near and away from ocean surface 14. Composite conduit 12
provides a high degree of nautical stability for the generally
mushroom-shaped structure 10 by penetrating to such extreme ocean
depths. In the description which follows, the equipment and system
structure size will pertain to an exemplary 100 megawatt net
electric system. It should be understood that, however, this same
system structure/packaging configuration can be utilized with
different sized components or that multiple structures having the
following description can, by utilizing a modular approach, be
integrated into a larger overall electrical generation-water
production system. Utilizing prestressed concrete for the OTEC
system structure 10 enables elimination of a separate supporting
platform since the prestressed concrete structure 10 simultaneously
provides outer casings for the system's components and functions as
a flotation device for maintaining system buoyancy within the body
of water. While other materials can be utilized to form the system
structure 10 and still obtain a high density power enclosure system
of 3,667 cubic meters per megawatt net electric output, prestressed
concrete is favored for its dual utility (containment and buoyancy)
and its low material and fabrication costs.
FIG. 2A is a sectional view of FIG. 1. Schematic crane 16 is
supported by system structure 10 and illustrates typical equipment
installation and/or removal positions therefor. Flash evaporator 18
has an outer casing 20 which generally constitutes a toroidal
surface. Toroidal casing 20 is radially disposed about vertical
axis 22. Axial flow steam turbine 24 has a rotor structure which
includes a vertical shaft 26 whose axis of rotation is
substantially coincident with vertical axis 22. The rotor structure
additionally includes disc portion 28 and blades 30 which
preferably constitute wound fiberglass filament. Disc 28 surrounds
shaft 26 and provides support for blades 30, which are attached to
the radially outer periphery thereof. Disc 28 is, by example,
approximately 32.7 meters in diameter and is preferably fabricated
as disclosed in A. Grijalba's commonly assigned copending patent
Application Ser. No. 918,125. Shaft 26 is, by example, rotatably
supported by exemplary 30 inch thrust bearings 32 and is coupled to
drive generator 34 and exciter 36 to produce, when rotated,
electrical energy. Condenser 38 is annularly disposed about
vertical axis 22 and is arranged to condense motive steam
exhausting from blades 30.
Relatively warm ocean surface water is drawn through radially outer
skirt-conduit structure 44 from a depth of approximately thirty
meters through inlet opening 46 into a radially outer portion of
evaporator 18's casing 20. The entering warm ocean water passes
over weir 48 onto an evaporator tray structure 49 constituting two
levels of evaporator trays 50 and 52, which are slightly slanted
downward and radially inward. Approximately one-half to one percent
of the warm ocean water passing over weir 48 flashes into steam and
passes through stepped moisture separator or demister structure 54,
while the remaining unflashed warm water flows radially inward and
exits evaporator 18 through drain outlet 56 disposed through a
radially inner portion of evaporator casing 20. Annular evaporator
drain outlet 56 provides fluid access to a second skirt-conduit
structure 58 which is circumferentially disposed about vertical
axis 22 and includes outlet conduits 59 which transmit the warm
water exiting drain outlet 56 to the ocean. FIG. 4 better
illustrates outer skirt 44, weir 48, and the evaporator trays 50
and 52. Radially inward flow of the warm ocean water is imparted by
weir 48 and associated evaporator tray structure 49 to minimize
thermodynamic non-equilibrium and maximize steam-water
separation.
At start-up time for the illustrated OTEC system, compressors
evacuate evaporators 18 so as to cause relatively warm seawater to
be drawn through conduits 44 and 59 into evaporator 18. Upon
reaching the desired seawater level in evaporator 18 propulsion
means such as pumps 60 begin to provide warm water circulation
through evaporator 18. Pumps 60 are illustrated within outlet
conduits 59 rather than in the inlet skirt conduits 44 to take
advantage of the Barometric Level Principle in supplying minimum
pumping power for the exemplary flow rate of 343 tons of water per
second.
After passing through demisters 54, the steam flows in a curved
path, generally radially inward, as represented by stream lines A
and passes through control port's 62 in cylindrical control wall
63. Control wall 63 preferably extends between evaporator casing 20
and skirt-conduit structure 58. A plurality of such ports 62 and
mateable control doors 64 are disposed circumferentially about
vertical axis 22 within evaporator 18. During normal operation of
the exemplary OTEC equipment, hinged control doors 64 are
maintained in the illustrated, open position by extending locking
pins 66 under the open doors 64 to obstruct closure thereof. When,
however, a turbine overspeed or other abnormal operating condition
occurs, control pins 66 are retracted, allowing control doors 64 to
close and obstruct ports 62 so as to prevent motive steam from
entering turbine 24. Turbine access control door 64 is better
illustrated in the operating position in FIG. 5A. Control pin 66
may be actuated to the releasing position by any suitable method
when one of the aforementioned abnormal conditions is detected. To
avoid upsetting normal flow equilibrium between evaporator 18 and
condenser 38, steam produced within evaporator 18 is bypassed to
the condenser 38 around turbine 24. Bypass steam flow, under such
conditions, generally follows the path indicated by stream lines B
in passing through a plurality of bypass ports 70 in skirt-conduit
58. Retraction of control pins 72 allow the normal pressure
differential between the evaporator and condenser to swing open
hinged bypass control doors 74. Control pins 72 are preferably
actuatable prior to control pins 66 to decrease the impact with
which turbine access control doors 64 close. Turbine bypass control
doors 74 are shown in the normal, closed operational configuration,
but can be seen in the open, bypassing state in FIG. 5B. Sealing
between access control doors 64 and control wall 63 and between
bypass control doors 74 and the radially inner wall of
skirt-conduit 58 is facilitated by interposing gaskets 76
therebetween as best illustrated in FIG. 5C. Control pins 66 and 72
are extended and retracted between obstructing and non-obstructing
door positions, preferably by fast actuating means, such as
electro-magnetic solenoid 78, as shown in FIGS. 5A, 5B, and 5C.
During normal operation, steam following stream lines A passes into
turbine inlet structure 79 through inlet ports 62 in wall 63.
Skirt-conduit structure 58 provides turbine 24 with a cylindrical
outer casing. A tapered inner casing structure 80 for turbine 24
includes portions 80a and 80b disposed upstream and downstream
respectively of disc 28. The outer periphery of disc 28 and the
base or platform of blades 30 cooperate with upstream and
downstream inner casing portions 80a and 80b to provide a
downwardly, radially inwardly tapered surface. The inner and outer
casings therebetween define an annular motive steam flow path of
increasing flow area in the downward axial direction. Turbine 24's
steam inlet structure 79 receives steam from inlet ports 62 and
includes radially inner wall 80a which redirects steam stream lines
A from a substantially radial direction to an axial direction.
Prior to entering rotatable blades 30, the motive steam passes
through stationary stator vanes 82 which impart a suitable flow
direction thereto compatible with entry into rotatable blades 30.
After expansion through rotatable blades 30, the motive steam is
exhausted through steam outlet structure 84 which includes
skirt-conduit/outer casing 58 and inner casing portion 80b. Due to
the diverging annular steam flow path through outlet structure 84,
diffusion of the steam flow obtains resulting in a slowing of the
exhausted steam and a partial conversion of its dynamic pressure
into static pressure prior to its entry into condenser 38. Steam
outlet structure 84 also includes inner, transverse decks, 85a and
85b which preferably house the previously mentioned evacuation
compressors and other auxiliary equipment. Transverse decks 85a and
85b also provide lateral support for inner casing portion 80b since
it is subjected to a vacuum on its radially outer side and
substantially atmospheric pressure on its radially inner side.
Inner casing portions 80a and 80b respectively include
substantially circular walls 80c and 80d which are disposed on
opposite axial sides of disc 28 and house bearings 32 which
rotatably support shaft 26.
FIGS. 2A and 2B illustrate alternate embodiments for condenser 38.
FIG. 2A illustrates vertical tubes 86 through which the motive
steam travels and within which it is condensed by radially flowing
cooling water which is segregated from the steam on the exterior of
the tubes. For illustration purposes the cooling water's stream
lines generally follow the paths indicated as C. The cooling water
constitutes relatively cold ocean water which is drawn from depths
of approximately 800 to 1,000 meters and is supplied to radially
inner inlet manifold 88 through conduit 12. Cooling water flows
radially outward through condenser 38 and across the exterior of
tubes 86, absorbing heat and causing the motive steam to condense
on the interior of tubes 86. At the radially outer edge of annular
condenser 38 the heat laden cooling water passes through outlet
manifold 90 into drain channel 91 both of which are included within
inner skirt-conduit structure 58. The heat laden cooling water is
transmitted axially downward in drain channel 91 back to the ocean
by propulsion means such as pumps 92. Condensate from the motive
steam drains vertically downward on the interior of tubes 86 into
condensate sump 94, where it is collected for subsequent
distribution.
Radially outer skirt-conduit structure 44 preferably constitutes
sixteen conduits 44a substantially uniformly distributed about axis
22 and a skirt member 94b which connects the included conduits. An
alternate embodiment for the skirt-conduit structure includes an
annular conduit 44c which also extends circumferentially about axis
22. The preferable and alternate skirt-conduit structures 44 are
respectively illustrated in FIGS. 6A and 6B which are partial
sectional views of FIG. 2A. Evaporator drain outlet 56 constitutes
an annular channel which feeds, by example, four evaporator outlet
conduits 59. Condenser drain channel 91, best shown in FIGS. 2A and
2B, preferably constitutes an annular passageway comprising part of
the skirt-conduit structure 58 and is circumferentially disposed
about axis 22 radially within evaporator drain outlet conduits 59.
The radially inner wall of skirt-conduit 59 is seen to provide the
radially outer casing of turbine 24.
FIG. 2B illustrates condenser 38 as having horizontal tubes 96,
which extend through radially inner tube sheets 98 and radially
outer tube sheets 100. In such configuration cooling water retains
the flow pattern indicated in FIG. 2A by stream lines C, but now
passes through the interior of tubes 96, causing motive steam
exhausted into condenser 38 to be condensed on the exterior of
tubes 96. The resulting condensate drains into annular sump 94 in a
similar manner to the embodiment of FIG. 2A.
FIG. 3 is a pictorial cutaway illustration of an inner portion of
the system structure shown in FIG. 2B. The bypass control doors 74
illustrated in FIG. 3 are hinged along their bottom rather than
their top as shown in FIG. 5B. Both bypass control door embodiments
are functionally acceptable to accomplish proper transmission of
bypass steam flow.
System structure 10 generally has a toroidal portion near its top
and a cylindrical portion extending down therefrom so as to
compositely resemble a mushroom. The toroidal evaporator casing 20
and generally cylindrical skirt-conduit/turbine casing 58 were
chosen and assembled to provide a composite structural shape which
is a compromise between conventionally constructed equipment
casings and the vessel of minimum wall thickness--a sphere.
Vertical, cylindrical bulkheads 101 and 102 are radially separated
and circumferentially disposed about axis 22 above toroidal casing
20 and turbine inlet structure 79. Annular decks 103 are
horizontally disposed between the bulkheads to provide rooms for
housing the OTEC structure's crew and equipment control facilities.
Access cover 104 disposed across the circular space bounded by
bulkhead 102 can be removed by crane 16 to facilitate repair and/or
maintenance of equipment components such as turbine 24, generator
34, and exciter 36. A judicious material choice for the complexly
shaped system structure 10 such as prestressed concrete permits
elimination of the conventional ship, hull or platform which was
heretofore considered an expensive component of the open cycle OTEC
system.
It will now be apparent that an improved OTEC open cycle power
system has been provided in which the power cycle's component
equipment casings structurally cooperate to simultaneously function
as a hull structure. The equipment casing's structural and
functional cooperation has reduced total plant capital cost for the
exemplary 100 MWE system to $1500 per net KW electrical output.
While the illustrated system is described as producing net
electrical output and distilled water as a valuable byproduct, it
is to be understood that component equipment size can be reduced to
provide zero net electrical output if water production alone is to
be economically maximized for a given system structure.
* * * * *